Re: [alsa-devel] Verifying mixer dB data/Invalid dB data from USB cards, especially Aureon 5.1 MkII

On Tue, 16.02.10 09:08, Clemens Ladisch (clemens@ladisch.de) wrote:

Lennart Poettering wrote:

...

Getting back to the invalid dB data from the USB cards: the question is whether the USB descriptor data is badly parsed, and the dB mismatch hence systematic for USB cards,

USB descriptors use units of 1/256th dB, while ALSA uses 1/100th dB. When the level is computed from the minimum plus a multiple of the step size, rounding errors add up considerately.

ALSA 1.0.21 (kernel 2.6.32) added a different TLV type that reports the range with the min/max values to minimize those rounding errors.

I am really sure that the discrepancy I measure with the Aureon is way beyond rounding errors.

Lennart